Synthesis and Investigation of a Soluble Distannene with no Trans-Bent Angle or Twisting in the Solid-State.

By treating KSiiPr3 with Sn[N(SiMe3)2]2 the distannene Sn2(TIPS)4 (TIPS=SiiPr3) is formed in a metathesis reaction. The crystal structure analysis of Sn2(TIPS)4 reveals a planar arrangement of the substituents in the solid-state and hence the second planar alkene like distannene of its kind. Due to the TIPS substituents, Sn2(TIPS)4 is well soluble in all commonly used organic solvents, opening the door for various analytics and reactivity studies. Due to its stability in solution, various reactions can be performed such as cycloaddition reactions with 2,3-dimethyl-1,3-butadiene (DMBD) and TMS-azide.

Synthesis of Cobalt-Tin and -Lead Tetrylidynes-Reactivity Study of the Triple Bond.

Tetrylidynes [TbbSn≡Co(PMe3 )3 ] (1 a) and [TbbPb≡Co(PMe3 )3 ] (2) (Tbb=2,6-[CH(SiMe3 )2 ]2 -4-(t-Bu)C6 H2 ) are accessed for the first time via a substitution reaction between [Na(OEt2 )][Co(PMe3 )4 ] and [Li(thf)2 ][TbbEBr2 ] (E=Sn, Pb). Following an alternative procedure the stannylidyne [Ar*Sn≡Co(PMe3 )3 ] (1 b) was synthesized by hydrogen atom abstraction using AIBN from the paramagnetic hydride complex [Ar*SnH=Co(PMe3 )3 ] (4) (AIBN=azobis(isobutyronitrile)). The stannylidyne 1 a adds two equivalents of water to yield the dihydroxide [TbbSn(OH)2 CoH2 (PMe3 )3 ] (5). In reaction of the stannylidyne 1 a with CO2 a product of a redox reaction [TbbSn(CO3 )Co(CO)(PMe3 )3 ] (6) was isolated. Protonation of the tetrylidynes occurs at the cobalt atom to give the metalla-stanna vinyl cation [TbbSn=CoH(PMe3 )3 ][BArF 4 ] (7 a) [ArF =C6 H3 -3,5-(CF3 )2 ]. The analogous germanium and tin cations [Ar*E=CoH(PMe3 )3 ][BArF 4 ] (E=Ge 9, Sn 7 b) (Ar*=C6 H3 (2,6-Trip)2 , Trip=2,4,6-C6 H2 iPr3 ) were also obtained by oxidation of the paramagnetic complexes [Ar*EH=Co(PMe3 )3 ] (E=Ge 3, Sn 4), which were synthesized by substitution of a PMe3 ligand of [Co(PMe3 )4 ] by a hydridoylene (Ar*EH) unit.

Authentic Sn═B-Double Bonds in Polar Stannaborene Derivatives.

We report on the synthesis of an authentic Sn═B-moiety realized in a stannaborenyl anion and stannaborenium cation. Starting with an oxidative addition of boron tribromide to a stannylene-phosphine Lewis pair [o-C6H4(Ar*BrSn-BBr2-PPh2)] (2a) [Ar* = C6H3(2,6-Trip)2, Trip = 2,4,6-C6H2iPr3] was synthesized. Reduction of 2a with magnesium yields the Grignard-type stannaborene [o-C6H4(Ar*Sn═B{PPh2}MgBr{thf})]2 (3)2 featuring a Sn═B double bond and a B-Mg interaction. Following an alternative protocol, hydride substitution at 2a yields the tinhydride [o-C6H4(Ar*HSn-BBr2-PPh2)] (4a). HBr elimination of 4a in reaction with MeNHC (MeNHC = 1,3,4,5-tetramethylimidazol-2-ylidene) gives the carbene and phosphine stabilized stannyl-borylene [o-C6H4(Ar*BrSn-B{PPh2}{MeNHC})] (5) after simultaneous bromide transfer from boron to tin. In reaction of 5 with Li[Al(OC{CF3}3)4] or Na[BArF4] in a mixture of o-DFB/benzene a stannaborene [o-C6H4(Ar*Sn═B{PPh2}{MeNHC})]+ [6] stabilized by the respective weakly coordinating anion was isolated (ArF = C6H3-3,5-(CF3)2, o-DFB = o-difluorobenzene). The phosphine and NHC-supported stannaborenium cation 6 adds ammonia at room temperature under splitting of a N-H bond and formation of Sn-NH2 and B-H bonds to give [o-C6H4(Ar*{H2N}Sn-BH{PPh2}{MeNHC})]+ (7).

Stiba-, Arsa- and Phosphastannenes: Syntheses and Reactivities.

A facile synthesis for unprecedented stibastannene (10) featuring a Sn=Sb-double bond together with the homologous arsa- (9) and phosphastannenes (8) is presented. Chloride abstraction from respective stannyl pnictinidenes [E=P (5), As (6), Sb (7)], which were made accessible by reduction of ECl3 addition products at an intramolecular phosphine-stabilized stannylene, gave the pnictastannenes in moderate yields. The pnictastannenes coordinate Pd(PPh3 )2 fragments (12-14) and the phosphastannene forms also a nickel coordination compound with the Ni(PPh3 )2 -fragment (11). 2,3-Dimethylbutadiene shows a [2+4]-cycloaddition (15-17) in reaction with the pnictastannenes (8-10). Products of a [2+2]-addition (18, 19) were isolated as the phosphaalkyne reaction products for 8 and 9. Addition of an O-H bond at the Sn=P-bond was found in reaction of water with phosphastannene 8. Reaction with ammonia afforded the NH3 -adducts (21-23) at the tin atom for pnictastannenes 8-10. Only in the case of the arsastannene an azide reaction product featuring a three membered Sn-As-N-ring was obtained.

Heavy metalla vinyl-cations show metal-Lewis acid cooperativity in reaction with small molecules (NH3, N2H4, H2O, H2).

Halide abstraction from tetrylidene complexes [TbbE(Br)IrH(PMe3)3] [E = Ge (1), Sn (2)] and [Ar*E(Cl)IrH(PMe3)3] gives the salts [TbbEIrH(PMe3)3][BArF 4] [E = Ge (3), Sn (4)] and [Ar*EIrH(PMe3)3][BArF 4] [E = Ge (3'), E = Sn (4')] (Tbb = 2,6-[CH(SiMe3)2]2-4-(t-Bu)C6H2, Ar* = 2,6-Trip2C6H3, Trip = 2,4,6-triisopropylphenyl). Bonding analysis suggests their most suitable description as metalla-tetrela vinyl cations with an Ir[double bond, length as m-dash]E double bond and a near linear coordination at the Ge/Sn atoms. Cationic complexes 3 and 4 oxidatively add NH3, N2H4, H2O, HCl, and H2 selectively to give: [TbbGe(NH2)IrH2(PMe3)3][BArF 4] (5), [TbbE(NHNH2)IrH2(PMe3)3][BArF 4] [E = Ge (7), Sn (8)], [TbbE(OH)IrH2(PMe3)3][BArF 4] [E = Ge (9), Sn (10)], [TbbE(Cl)IrH2(PMe3)3][BArF 4] [E = Ge (11a), Sn (12a)], [TbbGe(H)IrH2(PMe3)3][BArF 4] (13), [TbbSn(µ-H3)Ir(PMe3)3][BArF 4] (14), and [TbbSn(H)IrH2(PMe3)3][BArF 4] (15). 14 isomerizes to give 15via an 1,2-H shift reaction. Hydride addition to cation 3 gives a mixture of products [TbbGeHIrH(PMe3)3] (16) and [TbbGeIrH2(PMe3)3] (17) and a reversible 1,2-H shift between 16 and 17 was studied. In the tin case 4 the dihydride [TbbSnIrH2(PMe3)3] (18) was isolated exclusively. The PMe3 and PEt3 derivatives, 18 and [TbbSnIrH2(PEt3)3] (19), respectively, could also be synthesized in reaction of [TbbSnH2]- with the respective chloride [(R3P) n IrCl] (R = Me, n = 4; R = Et, n = 3). Reaction of complex 19 with CO gives the substitution product [TbbSnIrH2(CO)(PEt3)2] (20). Further reaction with CO results in hydrogen transfer from the iridium to the tin atom to give [TbbSnH2Ir(CO)2(PEt3)2] (21). The reversibility of this ligand induced reductive elimination transferring 20 to 21 is shown.

Boradigermaallyl: (4+3) Cycloaddition-Initiated Boron Insertion into Benzene.

The 2π electron 1,3-dipole boradigermaallyl, valence-isoelectronic to an allyl cation, is synthesized from a bis(germylene). It reacts with benzene at room temperature by insertion of a boron atom into the benzene ring. Computational investigation of the mechanism shows the boradigermaallyl reacting with a benzene molecule in a concerted (4+3) or [π4s+π2s] cycloaddition reaction. Thus, the boradigermaallyl acts as a highly reactive dienophile in this cycloaddition reaction with nonactivated benzene as diene unit. This type of reactivity provides a novel platform for ligand assisted borylene insertion chemistry.

Molecular Ln(III)-H-E(II) Linkages (Ln=Y, Lu; E=Ge, Sn, Pb).

Following the alkane-elimination route, the reaction between tetravalent aryl tintrihydride Ar*SnH3 and trivalent rare-earth-metallocene alkyls [Cp*2 Ln(CH{SiMe3 }2 )] gave complexes [Cp*2 Ln(µ-H)2 SnAr*] implementing a low-valent tin hydride (Ln=Y, Lu; Ar*=2,6-Trip2 C6 H3 , Trip=2,4,6-triisopropylphenyl). The homologous complexes of germanium and lead, [Cp*2 Ln(µ-H)2 EAr*] (E = Ge, Pb), were accessed via addition of low-valent [(Ar*EH)2 ] to the rare-earth-metal hydrides [(Cp*2 LnH)2 ]. The lead compounds [Cp*2 Ln(µ-H)2 PbAr*] exhibit H/D exchange in reactions with deuterated solvents or dihydrogen.

Hydridotetrylene [Ar*EH] (E = Ge, Sn, Pb) coordination at tantalum, tungsten, and zirconium.

In a reaction of tantalocene trihydride with the low valent aryl tin cation [Ar*Sn(C6H6)][Al(OC{CF3}3)4] (1a) the hydridostannylene complex [Cp2TaH2-Sn(H)Ar*][Al(OC{CF3}3)4] (2) was synthesized. Hydride bridged adducts [Cp2WH2EAr*][Al(OC{CF3}3)4] (E = Sn 3a, Pb 3b) were isolated as products of the reaction between Cp2WH2 and cations [Ar*E(C6H6)][Al(OC{CF3}3)4] (E = Sn 1a, Pb 1b). The tin adduct 3a exhibits a proton migration to give the hydridostannylene complex [Cp2W(H)[double bond, length as m-dash]Sn(H)Ar*][Al(OC{CF3}3)4] 4a. The cationic complex 4a is deprotonated at the tin atom in reaction with base MeNHC at 80 °C to give a hydrido-tungstenostannylene [Cp2W(H)SnAr*] 5a. Reprotonation of metallostannylene 5a with acid [H(Et2O)2][BArF] provides an alternative route to hydridotetrylene coordination. Complex 4a adds hydride to give the dihydrostannyl complex [Cp2W(H)-SnH2Ar*] (7). With styrene 4a shows formation of a hydrostannylation product [Cp2W(H)[double bond, length as m-dash]Sn(CH2CH2Ph)Ar*][Al(OC{CF3}3)4] (8). The lead adduct 3b was deprotonated with MeNHC to give plumbylene 5b [Cp2W(H)PbAr*]. Protonation of 5b with [H(Et2O)2][Al(OC{CF3}3)4] at -40 °C followed by low temperature NMR spectroscopy indicates a hydridoplumbylene intermediate [Cp2W(H)[double bond, length as m-dash]Pb(H)Ar*]+ (4b). Hydrido-tungstenotetrylenes of elements Ge (5c), Sn (5a) and Pb (5b) were also synthesized reacting the salt [Cp2W(H)Li]4 with organotetrylene halides. The metallogermylene [Cp2W(H)GeAr*] (5c) shows an isomerization via 1,2-H-migration to give the hydridogermylene [Cp2W[double bond, length as m-dash]Ge(H)Ar*] (9), which is accelerated by addition of AIBN. 9 is at rt photochemically transferred back to 5c under light of a mercury vapor lamp. Zirconocene dihydride [Cp2ZrH2]2 reacts with tin cation 1a to give the trinuclear hydridostannylene adduct 10 [({Cp2Zr}2{µ-H})(µ-H)2µ-Sn(H)Ar*][Al(OC{CF3}3)4]. Deprotonation of 10 was carried out using benzyl potassium to give neutral [({Cp2Zr}2{µ-H})(µ-H)µ-Sn(H)Ar*] (11). 11 was also obtained from the reaction of low valent tin hydride [Ar*SnH]2 with two equivalents of [Cp2ZrH2]2. The trihydride Ar*SnH3 reacts with half of an equivalent of [Cp2ZrH2]2 under evolution of hydrogen and formation of a dihydrostannyl complex 13 [Cp2Zr(µ-H)SnH2Ar*]2 and with further equivalents of Ar*SnH3 to give bis(hydridostannylene) complex [Cp2Zr{Sn(H)Ar*}2].

Reactivity of organogermanium and organotin trihydrides.

The organogermanium and organotin trihydrides (TbbEH3) [E = Ge (3), Sn (7)] with the Tbb substituent were synthesized by hydride substitution (Tbb = 2,6-[CH(SiMe3)2]2-4-(t-Bu)C6H2). Deprotonation of the organoelement trihydrides 3 and 7 was studied in reaction with bases MeLi, BnK and LDA (Bn = benzyl, LDA = lithium diisopropylamide) to yield the deprotonation products (8-11) as lithium or potassium salts. Hydride abstraction from TbbSnH3 using the trityl salt [Ph3C][Al(OC{CF3}3)4] gives the salt [TbbSnH2][Al(OC{CF3}3)4] (12) which was stabilized by thf donor ligands [TbbSnH2(thf)2][Al(OC{CF3}3)4] (13). Tintrihydride 7 reacts with trialkylamine Et2MeN to give as the product of a reductive elimination of hydrogen the distannane (TbbSnH2)2 (14). Transfer of hydrogen was observed in reaction of trihydrides TbbEH3 (E = Ge, Sn) and Ar*GeH3 with N-heterocyclic carbene (NHC). The NHC adduct TbbSnH(iPrNHC) (15) was synthesized at rt and the germanium hydrides exhibit hydrogen transfer at higher temperatures to give Ar*GeH(MeNHC) (16) and TbbGeH(MeNHC) (17).

Carbocyclic pincer carbene complexes of ruthenium: syntheses and reversible hydrogenation.

The ruthenium carbene pincer complex 2 was synthesized treating the benzo annulated cycloheptatriene bisphosphine 1 with RuCl3. Addition of three equivalents of hydrogen to the carbocyclic carbene complex 2 was achieved in reaction of 2 with hydrogen at elevated temperatures. Hydrogenated complex 4, exhibiting a rigid chair conformation in solution, was dehydrogenated by heating a toluene solution of complex 4 to reflux for 5-7 d. In reaction with ethylene, complex 4 transfers one equivalent of hydrogen, forming ethane and alkyl complex 5.

Phosphine-Stabilized Pnictinidenes.

The reaction of the intramolecular germylene-phosphine Lewis pair (o-PPh2 )C6 H4 GeAr* (1) with Group 15 element trichlorides ECl3 (E=P, As, Sb) was investigated. After oxidative addition, the resulting compounds (o-PPh2 )C6 H4 (Ar*)Ge(Cl)ECl2 (2: E=P, 3: E=As, 4: E=Sb) were reduced by using sodium metal or LiHBEt3 . The molecular structures of the phosphine-stabilized phosphinidene (o-PPh2 )C6 H4 (Ar*)Ge(Cl)P (5), arsinidene (o-PPh2 )C6 H4 (Ar*)Ge(Cl)As (6) and stibinidene (o-PPh2 )C6 H4 (Ar*)Ge(Cl)Sb (7) are presented; they feature a two-coordinate low-valent Group 15 element. After chloride abstraction, a cyclic germaphosphene [(o-PPh2 )C6 H4 (Ar*)GeP] [B(C6 H3 (CF3 )2 )4 ] (8) was isolated. The 31 P NMR data of the germaphosphene were compared with literature examples and analyzed by quantum chemical calculations. The phosphinidene was treated with [iBu2 AlH]2 , and the product of an Al-H addition to the low-valent phosphorus atom (o-PPh2 )C6 H4 (Ar*)Ge(H)P(H)Al(C4 H9 )2 (9) was characterized.

Phosphine-Stabilized Germasilenylidene: Source for a Silicon-Atom Transfer.

A phosphine-stabilized germasilenylidene is synthesized following the pathway of SiCl4 oxidative addition at a germylene-phosphine Lewis pair. Low-temperature reduction using {(MesNacnac)Mg}2 resulted in a chlorosilylene intermediate and finally a molecule exhibiting a Ge═Si: motif. Inside the chelating phosphine-germylene, a low-valent silicon atom is stabilized and was transferred to diazabutadiene to give N-heterocyclic silylenes. Because of the high reactivity of the phosphine-stabilized germasilenylidene, a reaction of two Ge═Si: units was found to yield a Si2Ge2-ring molecule exhibiting a germasilene substituted with a silylene.

Low valent lead and tin hydrides in reactions with heteroallenes.

Low valent organoelement hydrides of tin and lead, [(Ar*SnH)2] and [(Ar*PbH)2], were reacted with diorganocarbodiimide and adamantylisocyanate to give products of hydroelementation reactions. Carbon dioxide also reacts with both low valent hydrides, but a reaction product was only characterized in the tin hydride case. A hydride was transferred to the carbon atom and the formed formate anion [HCO2]- shows coordination at two tin atoms. Carbon disulfide reacts with the stannyl-stannylene isomer of the low valent organotin hydride. The stannyl part forms a Sn-C bond whereas the stannylene moiety coordinates at the two sulfur atoms. The dimeric organolead hydride exhibits transfer of both hydride ligands to the carbon atom of CS2 to give a dithiol ligand [CH2S2]2- bridging both organolead units.

Synthesis and Hydrogenation of Heavy Homologues of Rhodium Carbynes: [(Me3 P)2 (Ph3 P)Rh≡E-Ar*] (E=Sn, Pb).

Tetrylidynes [(Me3 P)2 (Ph3 P)Rh≡SnAr*] (10) and [(Me3 P)2 (Ph3 P)Rh≡PbAr*] (11) are accessed for the first time via dehydrogenation of dihydrides [(Ph3 P)2 RhH2 SnAr*] (3) and [(Ph3 P)2 RhH2 PbAr*] (7) (Ar*=2,6-Trip2 C6 H3 , Trip=2,4,6-triisopropylphenyl), respectively. Tin dihydride 3 was either synthesized in reaction of the dihydridostannate [Ar*SnH2 ]- with [(Ph3 P)3 RhCl] or via reaction between hydrides [(Ph3 P)3 RhH] and 1 / 2 [(Ar*SnH)2 ]. Homologous lead hydride [(Ph3 P)2 RhH2 PbAr*] (7) was synthesized analogously from [(Ph3 P)3 RhH] and 1 / 2 [(Ar*PbH)2 ]. Abstraction of hydrogen from 3 and 7 supported by styrene and trimethylphosphine addition yields tetrylidynes 10 and 11. Stannylidyne 10 was also characterized by 119 Sn Mössbauer spectroscopy. Hydrogenation of the triple bonds at room temperature with excess H2 gives the cis-dihydride [(Me3 P)2 (Ph3 P)RhH2 PbAr*] (12) and the tetrahydride [(Me3 P)2 (Ph3 P)RhH2 SnH2 Ar*] (14). Complex 14 eliminates spontaneously one equivalent of hydrogen at room temperature to give the dihydride [(Me3 P)2 (Ph3 P)RhH2 SnAr*] (13). Hydrogen addition and elimination at stannylene tin between complexes 13 and 14 is a reversible reaction at room temperature.

Germaborenes: Borylene Transfer Agents for the Synthesis of Iminoboranes.

Halide and phenyl substituted germaborenes were shown to react with azides at room temperature and transfer a borylene moiety to give iminoboranes. This iminoborane synthesis based on a borylene transfer route was investigated computationally in the case of the phenyl substituted germaborene.

Tetryl-Tetrylene Addition to Phenylacetylene.

Phenylacetylene adds [Ar*GeH2 -SnAr'], [Ar*GeH2 -PbAr'] and [Ar'SnH2 -PbAr*] at rt in a regioselective and stereoselective reaction. The highest reactivity was found for the stannylene, which reacts immediately upon addition of one equivalent of alkyne. However, the plumbylenes exhibit addition to the alkyne only in reaction with an excess of phenylacetylene. The product of the germylplumbylene addition reacts with a second equivalent of alkyne and the product of a CH-activation, a dimeric lead acetylide, were isolated. In the case of the stannylplumbylene the trans-addition product was characterized as the kinetically controlled product which isomerizes at rt to yield the cis-addition product, which is stabilized by an intramolecular Sn-H-Pb interaction. NMR chemical shifts of the olefins were investigated using two- and four-component relativistic DFT calculations, as spin-orbit effects can be large. Hydride abstraction was carried out by treating [Ar'SnPhC=CHGeH2 Ar*] with the trityl salt [Ph3 C][Al(OC{CF3 })4 ] to yield a four membered ring cation.

Conformation controlled stepwise hydride shuffling from the metal to the ligand backbone.

The benzo annulated cycloheptatriene PCP pincer ruthenium hydrido dicarbonyl complex syn-2 was prepared in one step by treatment of the ligand 1 with Ru3(CO)12. Protonation of syn-2 with the superacid [H(Et2O)2][BArF24] {[BArF24]- = tetrakis[bis(trifluoromethyl)phenyl]borate} initiates the highly stereoselective hydrogenation of one of the double bonds in the cycloheptatriene backbone. This results in the formation of the pentacoordinate cationic 16-electron dicarbonyl ruthenium complex 3. Hydrogenation of 3 with LiAlH4 generates the hydride complexes syn-4 and anti-4 which after protonation allow isolation of the symmetric 5. In 5 a second double bond of the cycloheptatriene backbone was hydrogenated. Complex 5 was also obtained directly by the reaction of 3 with hydrogen (1 bar). Storage of 5 under a hydrogen atmosphere yields two pairs of η2-H2 complexes (syn-7, anti-7) which are in a tautomeric equilibrium with their corresponding dihydrides (syn-8, anti-8). A stepwise transfer of the hydrides to the ligand backbone can be deduced from the distribution of deuterium along the seven membered ring after applying the deuterated reagents (D+, D2). The observed stereochemistry suggests that the hydride transfer is controlled by conformational constraints.

Ge=B π-Bonding: Synthesis and Reversible [2+2]†Cycloaddition of Germaborenes.

Phosphine-stabilized germaborenes featuring an unprecedented Ge=B double bond with short B⋅⋅⋅Ge contacts of 1.886(2) (4) and 1.895(3) Š(5) were synthesized starting from an intramolecular germylene-phosphine Lewis pair (1). After oxidative addition of boron trihalides BX3 (X=Cl, Br), the addition products were reduced with magnesium and catalytic amounts of anthracene to give the borylene derivatives in yields of 78 % (4) and 57 % (5). These halide-substituted germaborenes were characterized by single-crystal structure analysis, and the electronic structures were studied by quantum-chemical calculations. According to an NBO NRT analysis, the dominating Lewis structure contains a Ge=B double bond. The germaborenes undergo a reversible, photochemically initiated [2+2] cycloaddition with the phenyl moiety of a terphenyl substituent at room temperature, forming a complex heterocyclic structure with GeIV in a strongly distorted coordination environment.

Hydridoorganostannylene Coordination: Group 4 Metallocene Dichloride Reduction in Reaction with Organodihydridostannate Anions.

Organodihydridoelement anions of germanium and tin were reacted with metallocene dichlorides of Group 4 metals Ti, Zr and Hf. The germate anion [Ar*GeH2 ]- reacts with hafnocene dichloride under formation of the substitution product [Cp2 Hf(GeH2 Ar*)2 ]. Reaction of the organodihydridostannate with metallocene dichlorides affords the reduction products [Cp2 M(SnHAr*)2 ] (M=Ti, Zr, Hf). Abstraction of a hydride substituent from the titanium bis(hydridoorganostannylene) complex results in formation of cation [Cp2 M(SnAr*)(SnHAr*)]+ exhibiting a short Ti-Sn interaction. (Ar*=2,6-Trip2 C6 H3 , Trip=2,4,6-triisopropylphenyl).

Low valent lead hydride chemistry: hydroplumbylation of phenylacetylene and 1,1-dimethylallene.

Hydroplumbylation reactions of the low valent organolead hydride [(Ar*PbH)2] with phenylacetylene and 1,1-dimethylallene are presented. A vinyl plumbylene was isolated in the case of the alkyne reaction exhibiting a down field NMR signal for the CH unit attached to the low valent heavy atom. 1,1-Dimethylallene affords formation of an allyl plumbylene.